Abstract

The estimation of P- and S-wave arrival times is needed for many seismological applications, such as hypocenter location and Local Earthquake Tomography (LET). Automated methodologies are increasingly important as advances of seismic recording and the deployment of dense networks allow us to acquire large amounts of seismic data. Currently there are several methodologies available to estimate these arrival times. In this study, we adapted the REST technique of Comte et al. (2019) to detect phases and estimate onset arrival times from air gun shots recorded as part of the PICTURES project, a controlled-source seismic experiment conducted to investigate the crustal structure of the northern Chile region at the location of the 2014 Mw8.2 Iquique earthquake. A temporary onshore seismic network, composed of 50 short period (4.5 Hz), three-component, continuously recording stations, was able to record the air gun shots up to approximately 100 km. The signals generated by the shots are comparatively small as the study area is highly active seismically. Therefore, natural seismicity was one of the main impediments to identifying the onsets. Other factors include ambient noise and the distance from the source to the network. As part of the analysis, synthetic P- and S-phase arrivals were calculated for the shots at each station. Subsequently, waveforms for every event were extracted from the continuous data stream and filtered between 1 and 25 Hz. Finally, onsets and shot locations were estimated using a recursive algorithm. The events recovered with this procedure were then correlated with the shots based on the source time and location. We also identified and located around 8000 seismic events. The estimated P- and S-phases onset times will be used to improve previously determined 3D body wave velocity models in northern Chile.